Abstract

Background

Enterococcus faecalis, traditionally considered a harmless commensal of the intestinal tract, is now ranked
among the leading causes of nosocomial infections. In an attempt to gain insight into
the genetic make-up of commensal E. faecalis, we have studied genomic variation in a collection of community-derived E. faecalis isolated from the feces of Norwegian infants.

Results

The E. faecalis isolates were first sequence typed by multilocus sequence typing (MLST) and characterized
with respect to antibiotic resistance and properties associated with virulence. A
subset of the isolates was compared to the vancomycin resistant strain E. faecalis V583 (V583) by whole genome microarray comparison (comparative genomic hybridization
(CGH)). Several of the putative enterococcal virulence factors were found to be highly
prevalent among the commensal baby isolates. The genomic variation as observed by
CGH was less between isolates displaying the same MLST sequence type than between
isolates belonging to different evolutionary lineages.

Conclusion

The variations in gene content observed among the investigated commensal E. faecalis is comparable to the genetic variation previously reported among strains of various
origins thought to be representative of the major E. faecalis lineages. Previous MLST analysis of E. faecalis have identified so-called high-risk enterococcal clonal complexes (HiRECC), defined
as genetically distinct subpopulations, epidemiologically associated with enterococcal
infections. The observed correlation between CGH and MLST presented here, may offer
a method for the identification of lineage-specific genes, and may therefore add clues
on how to distinguish pathogenic from commensal E. faecalis. In this work, information on the core genome of E. faecalis is also substantially extended.